Để chế tạo lăng kính phản xạ toàn phần đặt trong không khí thì phải chọn thủy tinh để chiết suất là

A. n >  2

B. n >  3

C. n > 1,5

D.  3 > n >  2

a) 2 số đó có dạng a ; a + 1

ĐẶt UCLN(a ; a + 1) = d

a chia hết cho d

a + 1 chia hết cho d 

=> [(a + 1) - a] chia hết cho d

1 chia hết cho d => d = 1

Vậy 2 số tự nhiên liên tiếp là 2 số nguyên tố cùng nhau

Tương tự 

Indochinese Communist Youth League

Indochinese Democratic Youth League

Indochinese Youth League

Youth Union of Vietnam

Vietnamese Youth Workers' Union

Youth Union of Hồ Chí Minh

Hồ Chí Minh Communist Youth League

dễ thương quá

đáng yêu quá

bạn bấm cái này để biết kết quả nhé

https://hoc24.vn/hoi-dap/question/430878.html

I believe the best leisure activity for teenagers is any group activity. This could be playing a team sport or joining a hobby group or even volunteering. Firstly, teenagers like to feel that thev belong to the group. Secondly, being part of a group helps teenagers make friends. Friendship is very important to teenagers. In addition, they will make friends with people who have the same interests as them. For these reasons, I think group activities are best for teenagers.

Rewrite these sentences into tag question

1, Have you just used the computer ?

->You have just used the computer, haven't you?

2, Lan often listens to the radio, Doesn't she ?

->Lan often listens to the radio, Doesn't she ?

3. Are there many interesting programs tonight ?

-> there are many interesting programs tonight , aren't there?

4. Am I late for the party?

-> i late for the party, aren't I

5. Didn't Ba produce the first TV picture in 1920 ?

-> Ba did'n produce the first TV picture in 1920, did he?

6. Do they never go to the theater ?

-> they never go to the theater , don't they?

7. Is the pollution the most serious problem ?

-> the pollution is the most serious problem, isn't it

8. Do you do gymnastics every morning ?

-> you do gymnastics every morning, don't you

9. They do not do he washing up, don't they ?

-> They do not do he washing up, don't they ?

10. Mary won't come the party, will she ?

-> Mary won't come the party, will she ?

11. Tim and Bob drove to work last tern, didn't they ?

-> Tim and Bob drove to work last tern, didn't they ?

Section I: choose the word which has the underlined part pronounced differently from the other

1. A. School B. Chair C. Chemistry D. Character

2. A. Serious B. Symptom C. Sugar D. Sauce

3. A. Order B. Novel C. Portable D. Score

4. A.coop B. Cartoon C. Stool D. Indoors

Section II choose the word that has different stress from others

1. A. Complete B. Detective C. Gather C. Event

2. A. Mixture B. Allow C. Affect D. Disease

3. A. Exit B. Cushion C. Turtle D. Improve

4. A. Museum B. Useful C. Cavity D. Wedding

Section I: choose the best answer from A, B, C or D to fill in the gaps

1. She is staying....... her uncle and aunt's house

A. At B. In C. With D. On

2. Their trip to da lat...... wonderful

A. Was B. Were C. Are D. Is

3. There is...... meat in the box

A. Any B. A few C. A little D. Many

4. A. Don't forget.... your teeth before going to bed

A. Brush B. To brush C. Brushing D. Not to brush

5. You.... stay at home when you are sick

A. Had better B. Should C. Mustn't D. A and B

6. He doesn't like candy. I...,

A. Don't too B. Don't, either C. Don't neither D. Do so

7. I divided the sweets.... several boys

A. During B. Between C. Into D. Among

8. He was only ten, but he ate.... his father did

A. As much as B. More that C. Much than D. As much than